DESCRIPTION (Adapted from applicant's description): Studies of early cognitive functioning indicate that infants are capable of inventing strategies for solving novel problems and of generalizing the strategies to unfamiliar problems. However, virtually nothing is known about how they accomplish these feats. To address these issues, the investigators plan to obtain trial-by-trial assessments of infants' problem solving, and 2-year-olds will be presented problems requiring the choice of an appropriate tool for bringing a toy within reach. In each experiment, the infants will encounter a series of isomorphic problems, varying in their features but sharing goal structures and solution strategies. Microgenetic methods, involving intensive observation of problem-solving activities from the initial use of a strategy to its consistent use, will be used to identify when the first use of a new strategy occurs. This identification, in turn, will allow determination of the circumstances that led up to the discovery and of their generalization of the strategy beyond this initial context. Obtaining trial-by-trial data will allow accurate assessments of infants' strategies and of developmental differences in the rate and breadth of their learning. It will also allow examination of factors influencing infants' discovery and generalization of strategies.